The structure of surface layer above sea

Chalikov D.V., Bulgakov K.Yu.

The one-dimensional model of boundary layer above sea waves is suggested. The model is based on results obtained before with two-dimensional coupled model of wind and waves. The boundary layer above waves is different of model above flat surface by appearance of additional momentum flux created directly by curvilinear and moving interface. The one-dimensional equations of wave boundary layer can be derived in curvilinear surface-following coordinate system. In this case the equations contain explicitly the specifics of wave boundary layer. The momentum exchange between wind and waves is calculated in spectral space as a sum of separate fluxes, produced by wave modes. It is traditionally suggested that momentum flux is proportional to spectral density of wave energy with coefficient depending on wave age of each mode. The calculations illustrating the specific features of wave boundary layer: velocity and energy of turbulence profiles, wave and turbulent fluxes of momentum. The ratio of external (at upper level of boundary layer) and internal (at surface) roughness parameters is discussed. It is shown that external drag coefficient depends not only on wind velocity but also on shape of wave spectrum, what explains the large scatter of experimental data. Further development of suggested approach for problems of geophysical fluid mechanics is discussed. Such models are intended for coupling of atmosphere and ocean models with wave forecasting models.

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